NEW YORK (Reuters Health) - Food allergies may send more Americans to emergency rooms each year than commonly believed, a new study suggests.

Between 2001 and 2005, researchers estimate that Americans made just over a million visits to the ER for allergic reactions to food.

That averages out to about 200,000 ER trips each year, including an estimated 90,000 visits for serious, sometimes life-threatening, allergic reactions known as anaphylaxis.

Based on a study from the 1990s, 30,000 has been the often-quoted statistic typically given for how many Americans are sent to the ER each year by food-triggered anaphylaxis.

These latest findings, reported in the Journal of Allergy and Clinical Immunology, suggest that the numbers are now significantly higher.

"While severe, life-threatening food-related allergic reactions are still relatively uncommon, our study suggests that they are more common than previously thought," lead researcher Sunday Clark, of the University of Pittsburgh in Pennsylvania, told Reuters Health in an e-mail.

What's more, the findings suggest that ER visits for all levels of allergic reaction to food are more common than past studies have indicated.

One recent report, for example, estimated that Americans made 125,000 trips to the ER for food allergies in 2003, with about 14,000 of those involving anaphylaxis.

The current study and its bigger numbers are based on different data sources than those earlier analyses. Clark said her team used figures from an annual government survey of hospitals, along with two recent medical studies, to estimate the frequency of ER visits for true food allergies.

But it's also possible that a growing number of Americans have been heading to the ER for food reactions in more recent years, according to Clark.

In a study published earlier this year, she and her colleagues found evidence that more children are turning up in ERs with serious food reactions than in years past.

The number of food-induced allergic reactions treated at Children's Hospital Boston, for example, more than doubled over six years -- from 164 cases in 2001, to 391 in 2006.

The researchers were not able to tell why those figures rose. But they noted that the increase was in line with the national increase in the number of children being diagnosed with food allergies.

According to the U.S. Centers for Disease Control and Prevention, three million school-aged children in the U.S. had a food allergy in 2007, which was up 18 percent from 10 years earlier.

No one is sure why food allergies are being diagnosed more frequently. One theory is that changes in kids' diets are a contributor. Another theory, known as the "hygiene hypothesis," holds that modern cleanliness provides less exposure to germs early in life and may make the immune system more prone to attack normally benign substances, including food proteins.

The most common triggers of food allergies include milk, eggs, soy, wheat, shellfish, peanuts and tree nuts, like almonds, walnuts and cashews.

Clark said that the current findings underscore the importance of recognizing the signs of food-induced allergic reactions -- especially anaphylaxis, which requires emergency treatment.

Food allergy symptoms range from the relatively mild -- limited to problems like tingling in the mouth, hives or upset stomach -- to the more severe signs of anaphylaxis. Those include dizziness or fainting, difficulty breathing and a sudden drop in blood pressure that can lead to shock.